


Deception's Consent

by LazySintastic13 (EmeraldWriter)



Category: Undertale (Video Game)
Genre: Alternate Universe - Underfell, Cunnilingus, Dirty Talk, M/M, Overstimulation, Sex Toys, Somnophilia, Underfell Sans, kustard - Freeform, slightly consensual/non-consensual
Language: English
Status: Completed
Published: 2017-03-26
Updated: 2017-03-26
Packaged: 2018-10-10 19:37:43
Rating: Explicit
Warnings: Creator Chose Not To Use Archive Warnings
Chapters: 1
Words: 4,156
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/10445865
Author URL: https://archiveofourown.org/users/EmeraldWriter/pseuds/LazySintastic13
Summary: Red was a heavy sleeper. This Sans knew very well. And it just wouldn’t do to not take that to his advantage.Warnings: slightly consensual/non-consensual, somnophilia?, sex toy used, overstimulation, cunnilingus, dirty talk (I tried)





	

“So you’re sleeping here tonight?” Sans poked at his bowl of half-eaten spaghetti courtesy of his brother making it for them before he had left to go to some royal guard training and won’t be back in three days.

“Yeah, don’t really want to be at home and hear Boss nag to me about my incompetence—like always.” Red rolled his eye lights, earning him a soft chuckle from his counterpart.

“That’s a Papyrus for you.” Sans laughed some more, appearing quite nonchalantly on the surface. Though on the inside, he can feel his soul thrum at the thought of his partner staying over as it wasn’t often the other does so.

However, having the skeleton stay over is not the only reason why he was excited. There’s something more to it. A dirty secret he kept a tight hold of—a secret only he knew.

“No kidding. Anyway, let’s finish up. I’m getting really fucking sleepy.” To prove so, Red let out a huge yawn. Contagious enough that Sans did the same.

“You’re right. I’m pretty bone-tired myself.”

Red huffed, “That was weak.”

“But you’re smiling.”

“Whatever.” Red playfully hit the other’s shoulder as he gathered his plate and moved to put in the sink.

They were dating for almost two years now. Sans couldn’t believe they lasted this long after the rough start they had.

They fought the first time they met. Their views were very different. And the only thing they had in common was the love for puns, for science, and for their brothers. Other than that, they clashed often. Often enough that overtime, they understood each other; accepted one another—knew more than just the surface.

The atmosphere around them changed to that of companionship. It eventually led to a tension that both were too scared to tread on. And it was Sans that initiated it.

Here they were now. Not exactly lovey-dovey. Stars no, they didn’t need that shit. The dog couple had that covered. No. What they have is something much calmer—more at ease with being around one another. Not afraid to deny or accept the affection they throw at each other. Not afraid to point out when one is wrong or need to apologize for taking it too far. They were taking it slow.

In Sans’ opinion; however, it was too slow. It was almost two years after all, but they already had so much history even before that. He wanted to do more than just cuddle, more than the soft and sweet kisses here and there. He desired so much more. And he didn’t know if he was being greedy and selfish for thinking that way.  

It didn’t take them long to clean up their mess, a miracle their brothers will never bear witness to, and got ready for bed.

“Alright, turning in. ‘Night, Sans.” Red leaned in close to plant a chaste kiss on his lover’s mouth.

Sans craved to do so many things. He wanted to pull him closer, wrap his arms around Red’s waist. Open Red’s mouth to snake his tongue inside and meld with the other’s own slippery make-shift organ. Or maybe he preferred push Red to the wall so he can be rougher.

But he didn’t.

Instead, he settled for returning the kiss with a quick peck as well. Goodnight kisses are not supposed to linger. They were quick. Sans didn’t like them much to be honest.

“Goodnight, Red.”

They parted ways for they slept in different rooms instead of sharing a bed.

It was Sans’ who suggested the idea, more for his sanity and self-control than anything else. Red had questioned him a lot about it at first before conceding. They never pry and respected each other’s space. They work well with telling things to each other at their own time and pace.

Once Sans entered his room and closed the door, he leaned back and slid down to the floor. He sighed heavily, putting his head on the metacarpals of his hands. His thoughts were getting out of control again. Stars, but he couldn’t help it. Not when he was going to commit another immoral act.

Sans trudged towards his bed and laid down, not bothering to wrap the covers around himself. It was only a matter of time before he had to get up again anyway. He’d only had to wait.

* * *

Sans slowly crept into the room. While he could just teleport, it would always make a noise whenever it happens. He didn’t want to risk it. Even if Red was a heavy sleeper.

Stars. Red was _really_ a heavy sleeper.

He shouldn’t be taking advantage of his boyfriend like this. Then again, this wouldn’t be happening if it weren’t for that one time Sans had decided to be bold in relieving himself whilst they had been sharing a bed beforehand.

He was so pent up. And Sans didn’t want to make Red feel like he was rushing him into something he may not like, but by doing so, his sexual frustration just continued to build up. He needed release and one night, he had been too lazy to get up to the bathroom to take care of it. Instead, he reasoned with himself that he would be quiet enough to not disturb Red. His hand slowly travelled down and went inside his shorts to take out his already straining length and began to stroke it.

It had been so long. He was so caught up with the sensations that as Sans was reaching his peak, he didn’t expect for Red to turn exactly at that moment. It was too late for Sans to stop as he was facing Red’s figure.

He ended up ejaculating on Red’s face.

The sight of his fluids, more so when some had slid down to Red’s mouth, had his soul thumping hard against his rib cage and a sense of euphoria washed over his body. Sans’ eyes widened when the latter unconsciously opened their mouth and summoned a red translucent appendage to lick it. It was absolutely mesmerizing.

It was moments later that Sans had remembered that he should be cleaning up that took him out of his stupor.

Ever since that day, Sans began his nightly experiments. It started slow. He would come on Red’s face, then directly in his mouth, leading to start the small touches–caresses, and as the nights progressed, it eventually led to where he was now.

He quietly went to the front of the bed.

Sans could see that the blanket was the only thing covering everything below past where the sternum would be beneath the shirt. Just as he had done other nights, he slowly took off the covers.

His eye sockets widened at the sight. Red was _only_ wearing his shirt. And more than that, his eye lights travelled downward to the other’s pelvic area where he saw Red’s already formed genital. And there was a _dildo_ inside of him.

 _Oh my stars._ Sans swallowed nervously. He could sense his soul wanting to burst out as it began to glow and increase in beat.

He admired the view of his half naked lover sprawled out on the bed with the toy tucked inside of him. Though he never have fantasized about Red doing such a thing before, he now recognized that the sight before him was causing his magic to respond on his lower half.

Sans was amazed how Red’s folds spread around the thick circumference of the shaft. It stretched tightly to allow the thick rubber cock inside of him. 

His eyes slightly travelled upward to the top of the opening where he could see the distinct bump. 

His soul was pounding so loud that he could hear no other noise as he reached out.

His finger gently touched the cold rubber. Then, he wrapped his fingers around the base of the dildo. Sans tried to calm his nerves but despite his best efforts, his hand shook uncontrollably. He was too excited. 

At first, the toy offered resistance to his unsteady hand, but it eventually gave way from his shaking as he felt it move. It was almost imperceptible, but he felt it budge nonetheless.

Sans looked up quickly when he heard a soft whimper escape Red’s mouth and noticed his hips shift. Red was a heavy sleeper, but maybe this time, because of the toy inside of him, he would wake up. Stars, he would wake up, and Sans was going to be caught red-handed. 

If Red really did wake up now, Sans knew that he was dead. Their relationship would be over no doubt. And just the thought of it sent his mind into a spiral of panic.

Frozen like a deer caught in headlights he remained still as he focused on Red’s facial expressions whilst still holding onto the cock buried inside—unable to move. As suddenly as it had occurred; however, the fear of being caught dissipated. Sans realized that the other had merely shifted in his sleep and hadn’t woken up after all.

Sans leaned forward to ensure that Red’s eyes were still indeed, in fact, closed. He was filled with relief when he reassured himself that his lover was still out.

He shifted his attention back to his hand only to realize that by leaning forward, he had inadvertently pushed his hand forward as well, causing the dildo to move further inside of Red. 

Sans looked at his hand, the item that it held, and the pussy that seemed to be begging for more of it. As if propelled by some outside force, his hand nudged the rubber cock forward again. There was still a bit more of the shaft to put in and Sans marvelled at how easily it slid. He gave it another gentle nudge, watching as it slowly disappeared. 

The skeleton watched anxiously as the folds molded to the contours and bumps of the object as he pressed on. Then, he slowly reversed his course from pushing to pulling. It was riveting to see the glistening rubber emerge. 

Sans’ eyes moved up to Red’s body as he slowly removed the massive rubber cock. He could see the other’s breathing was getting heavier, even if only slightly, and was alert to the subtle movement of the rib cage with each breath. 

Sans realized that his partner’s body was responding to the stimulus. And it suddenly dawned on him that he was fucking Red with a _sex toy_. It was more than he’d ever done without consent. 

He didn’t know if this was classified as going too far, though when he looked back at Red, he rationalized to himself that the latter would _never_ even know what he was doing. Also, he was just finishing what Red had already started. What kind of a lover was he if he couldn’t help with that? Armed with an enough of an excuse to pacify his conscience, Sans proceeded to push the dildo back in. 

He repositioned himself so that he now partially sat on the bed in between Red’s legs, allowing him to move closer. From this position, Sans could now smell the heady aroma of the other’s sex. He leaned forward to take in the smell; his face merely inches away from the glistening magic as he inhaled. His cheek lightly grazed a femur as he traced it lightly with his tongue.  

The shaft was now pushed back to where it had been in its original state. In fact, he didn’t know how much more of it would fit inside and he felt delirious when he decided to find out and press on. Sans was quite amazed at Red’s size of choice and wondered how often he did it without him knowing. Maybe even he had been doing it before he even met Sans. The image of Red wrecking himself with a fake cock desperately begging for a real one sent a shiver down his spine. 

The skeleton moved his mouth so that it was now just an inch away from the clit evidently protruding out. His eyes were fixed on the target before him as he continued to slowly work the dildo. 

While he had been so focused on the sight, when Sans felt his fingers against the soft mound of magic, he realized with awe that he had successfully pushed the entire gigantic length inside of Red. And the latter still continued to _sleep_. 

_Geez, Red. I didn’t think you’d be quite the whore. You took it like a champ. Fuck._

Moving very carefully, Sans slowly pressed his lips gently against the nub. He could hear another soft moan as his mouth made contact with it. 

Needing to feel more, Sans pushed his tongue out so he could now taste the sweet nectar of his boyfriend’s juices. A shock of electricity coursed through his body as he ran his tongue against the small sensitive ball of magic. 

Sans twisted his head up to catch sight of the reactions he was making the latter feel, continuing to massage with his tongue. He could see Red’s chest move faster and noticed the glow of the other’s soul against it were now much more pronounced. 

Unable to stop himself, Sans continually increased the pressure and could feel Red’s hips begin to stir beneath him. Feeling bolder, Sans began to thrust into his lover with the fake cock faster. He followed after Red’s hip movement when it lifted up just slightly; it was enough to signal Sans of an incoming climax. 

He looked up at Red as he felt a small gush of fluids hindered by the toy hit his jaw. Sans slowed his hand as the body shuddered. He could see the thin sheen layer of sweat on Red’s face and how he was softly panting. 

Sans should have been too far gone to care if the latter does wake at this point, but he still held on to his self-control that, he was inwardly surprised, still existed. He continued to gently nibble at the nub while he allowed his partner time to recover from his orgasm. Sans was in no rush. He was happy that he made Red come. He always was. 

Sans eventually propped himself up, still sitting between the legs, and looked down at the sex toy tucked inside. He decided that it was time to finally remove it and slowly began to pull it out. 

Sans took his time and again watched carefully as the lips of the pussy molded to the contours of the shaft. He was once again struck by its size as he finally held it in his hand. It was much heavier than he imagined. It hung to a side, unable to support its own weight.

As he stared at the object, Sans began finding it unfair that something else that wasn’t his cock was taking his place. He placed it on the bed, looking back at the still twitching mound. Its juices oozed out from its hole as the lips were slightly separated from being stretched. It took Sans breath away.

“ _Fuck_. I didn’t know you were this _naughty_ , Red. Having toys like these.” He situated himself back, closer to the pulsating pussy.

“You tasted good. Did you know?” He made his point by licking around his mouth to get the fluids he missed. “And I’m so thirsty.” He chuckled softly when he heard a quick intake of breath the moment he circled a finger around the clit. He didn’t need to worry about any noises Red made anymore, they were involuntary reactions. It made it all the more arousing and thrilling for Sans. 

“You’re dripping _so much_. All for me, perhaps?”

He spread the folds wide as he flattened his tongue and began with slow and long licks, sliding the organ from the base to the top. He did this several times, enjoying the sight of Red’s pussy continuing to flood and decided then that it was time to delve into the main course.

“Well then, _bone-appetit_.”

Sans pushed his tongue into the hole, swirling it around to taste and slurp at Red’s essence.

Sans truly loved how Red reacted. The noises he made, the gripping of the sheets and the trembling of his legs as his pussy tighten and convulse around his tongue. _And yet_ , Red was still asleep. It was glorious.

It wouldn’t take long for Red to squirt again, knowing that the latter was most likely still sensitive. He was feeling quite proud of the fact that he was about to make him reach his peak once more. The skeleton decided to help out by putting in more magic in his appendage and made it _longer_ and _wider_ , pushing his tongue deep and braced himself when he felt the inner canals contract against him. Sans sensed that this was a more intense orgasm than the first and allowed it to run its course before pulling his mouth away. Red’s juices covered his mouth and he made sure to savor its unique taste.

He could feel his magic forming in his shorts and took no time to release his stiffening length standing proudly at full attention. He groaned when he gave it a squeeze. However, that wasn’t what he wanted to focus on.

As he stated before, Red was a deep sleeper, but thrusting his cock inside of him would surely wake him up this time. The overstimulation would be too much. Sans was certain he’d be rough if did it, and Red would wake. But stars, he was starting to lose control of his inhibitions. Especially since Red’s insides were contracting so enticingly—searching for something to fill it in. It wanted _his_ cock.

“Your body is so honest. It wants something to fill it up.” He began stroking the shaft. “I could that, you know? It would be so easy. But then you’d wake up … But maybe. Maybe I _want_ you to wake up.” He began moving faster. “The _look_ on your face … You’d probably be surprised to find my cock inside of you. Oh stars, but you’ll still take it, wouldn’t _you_?” He was panting now, his chest rising along with his movements.

“You’ll take it like the _slut_ you are.”

He rubbed the tip at Red’s entrance. “Oh _stars_. Red you’d feel so good. Look at that. You’re taking my cock so well.” The constant rubbing of the slippery and warm folds and the thrill of how easy it would be to just shove it in was bringing Sans over the edge. He didn’t realize that his rough movements were making the head of his cock actually push inside of Red’s entrance as his eyes were closed—too caught up with the sensation.

“ _Fuck!_ I’m going to—I’m going to come. Take it, take it, _take it, you slut!_ “ Sans spurted a large amount, not knowing that he had just unloaded inside of Red until he opened his eyes.

“Oh fuck.” Sans quickly pulled his cock out, albeit sluggishly as he was still feeling the euphoria from his climax. Sans was filled with an odd sense of satisfaction as he stared in awe at seeing his spunk drip out. He shook his head to clear it. He needed to look for anything to clean up the mess.

He decided that his shirt would do. The skeleton could just explain to Red in the morning if the latter even noticed that he had went downstairs for a drink but spilled it. Once he took it off, his eye lights caught sight of the glistening dildo, and a _horrible_ idea came to mind.

Maybe … Maybe he could just …

He could just hide the evidence by plugging the toy back inside.

Red’s magic would dissipate by the time he’d wake up, and he’d probably just think that it was his fluids instead Sans when it dried up. Besides, the latter would also be taking a shower in the morning and will then erase any evidence concerning him.

With that reasoning, Sans took the plastic cock and plugged it back inside Red. He rubbed the tip of the rubber cock in the growing pool of his come that was appearing at the opening. Slowly, he pushed the length in and pushed it as far into Red as he could manage, with the idea that it would in turn push his spunk deep enough that it would not seep out. The skeleton wiped the excess he couldn’t get inside and situated Red his, more or less, original position.

After having done the deed, Sans stood up and quietly left the room in the similar fashion he entered.

He didn’t get much sleep that night; too caught up in feeling apprehension, guilt, shame, but at the same time, he also sensed excitement and contentment fill his thrumming soul.

* * *

The next morning, Sans was nervous. He always was after his escapades, but more so than usual since he was still concerned about Red finding out what he’s done. He knew the other would know once they take it out. Stars, he was doomed without a doubt.

Taking a deep breath to ease the erratic pounding of his soul, Sans came out of his room and was met with Red doing the same.

“G’morning.” Red yawned widely, rubbing an eye socket to rid of his sleepiness.

“Heh, morning.” _Good, act natural._ “Had a good sleep?” _Oh my stars, I’m practically_ asking _for it._

He was surprised that Red was instead quite nonchalant, “Yeah, it was pretty great.” He smiled lazily at his lover. “A bit tired still though. Anyway, gonna use the bathroom first.”

“Uh, yeah! No problem. I’ll go ahead and make us some breakfast?”

“Sounds great.” Red kissed Sans on the cheek and left him to his muddled thoughts.

Sans didn’t know that he was holding his breath before he let out a sigh of relief. Red didn’t give any indication that anything happened last night, so he guessed that he was in the clear still. Sans should have been relieved but he couldn’t help feeling disappointed at the same time, wanting a reaction all the same. Maybe he wanted to get caught after all. Sans shook his head, he was starting to lose to his desires again.

Though, if Red’s been ‘entertaining’ himself on his own, Sans doesn’t know how long he will be able to hold out in actually fucking Red on a mattress soon. “Geez, Red is such a heavy sleeper.”

* * *

Meanwhile, Red was in the bathroom.

He situated himself on the toilet and braced himself on the lid as he slowly pulled the dildo out. A gush of thick blue liquid flowed out of him until it turned into little trickles. Some of it landed on the hand he was pulling the object out with.

Red chuckled as he licked at the remnants on the shaft, tasting its distinctive flavor that made him shudder in delight.

He had always been a light sleeper.

He had only been pretending for Sans’ sake at first, but now, with it happening constantly, Red enjoyed the excitement it brought. To be rendered unable to do a thing, and just take what Sans decided to give him offered him a rush of euphoria. Stars, he craved for it—craved for Sans to take charge.

And last night, Red was sure he was about to get discovered with all the movements he made. Sans had been particularly quite brutal in this session, making him oversensitive and come twice at that. Not that he didn’t enjoy it—quite the opposite.

Red clicked his tongue; however, he had been so close in making Sans fuck him while he was in his ‘sleep’.

“Heh, I didn’t think he still had any self-control left.” Red thought for sure that Sans would break his restraints when he saw his toy, but he was close. He looked at the fluids on his hand and gave it small licks. Then he proceeded to suck it off, making sure he’s gotten all of it. He moaned at the tangy-sweet taste.

“How dare you spurt inside but not fuck me, Sans. Talk about rude.” Red huffed lightly, though the grin was evident in his features.

Instead of cleaning Sans’ essence out of him completely, Red adjusted the toy’s size with his magic. Making it a bit thicker and longer and slowly pushed it back inside of him.

He was sure that tonight, Sans was going to fuck him. This time for sure.

Red looked at the mirror, adjusting his clothes and walked back and forth to get used to the sensation of the object inside of him. When he deemed himself presentable, he washed his face and got ready to face his ‘frustrated’ lover.

Pretending to be asleep was hard but the benefits in return were worth it. It was a dirty little secret—a secret only he knew.

**Author's Note:**

> Aaaaaaaaaahhhhhh!!! My kinks. omg. Hngh! XS
> 
> This was technically my first NSFW fic for the fandom and it was Kustard too. Jeebus. ^^”


End file.
